The invention relates to a fuel supply controller for an internal-combustion engine and, more specifically to a fuel supply controller capable of properly controlling the fuel supply rate in accelerating the engine.
Japanese Patent Document No. 54-134227 discloses a fuel supply controller for an internal-combustion engine. This known fuel supply controller supplies fuel to an engine at a basic fuel supply rate corresponding to the operating mode of the engine. It implements accelerating incremental fuel supply correction to enhance engine output for desired accelerating characteristics, when the engine is in a predetermined mode of acceleration, for example, when the variation of throttle valve position exceeds a fixed value. However, a disadvantage of this known fuel supply controller is that fuel is supplied to the engine at an excessively high fuel supply rate in accelerating the engine causing deterioration of engine performance and specific fuel consumption. In addition, the engine output decreases when fuel supplied thereto for each combustion cycle exceeds a maximum fuel supply rate. Furthermore, the higher the engine speed, the higher is the basic fuel supply rate to generate a higher engine output. On the other hand, since this known fuel supply controller is designed to set an accelerating incremental fuel supply rate regardless of the engine speed, it possible that the sum of the basic fuel supply rate and the accelerating incremental fuel supply rate will exceed the maximum fuel supply rate. In this event, fuel is supplied to the engine at such an excessively high fuel supply rate that output is reduced.
The fuel supply controller of Japanese Patent Document No. 54-134227 increases fuel supply in accelerating the engine, and then inhibits accelerating incremental fuel supply correction for a fixed period of time after accelerating incremental fuel supply correction has been implemented.
Since this known fuel supply controller inhibits further accelerating incremental fuel supply correction indiscriminately for a fixed period of time once accelerating incremental fuel supply correction is implemented, the fuel supply control operation of the fuel supply controller is unaffected by external disturbances such as noise. However, in some cases, such inhibition of further accelerating incremental fuel supply correction hinders the accelerating performance of the engine. In the case of a vehicle in which rapid acceleration performance is essential, such as a motorcycle, it is impossible with this known controller to control the fuel supply properly for rapid acceleration. The fuel supply (at an appropriate fuel supply rate) is delayed when accelerating operation is performed again before the elapse of the accelerating incremental fuel supply correction inhibiting period. This occurs because increasing the fuel supply rate is inhibited indiscriminately during the accelerating incremental fuel supply correction inhibiting period.
With respect to motorcycles in particular, it is possible to immediately close the throttle valve forcibly by turning the throttle grip. In contrast the throttle valve of an automobile is operated by stepping on the accelerator pedal and releasing the accelerating pedal. Hence, the throttle valve returns to the closed position spontaneously, in a predetermined time after the accelerator pedal has been released. Accordingly, the throttle valve of a motorcycle can immediately be closed after accelerating and can immediately be opened again, one of the features of a motorcycle. However, if accelerating incremental fuel supply correction is inhibited indiscriminately once accelerating fuel incremental supply correction has been implemented, it is impossible to take full advantage of this motorcycle feature.
Japanese Patent Document No. 61-15261 discloses a fuel supply controller for improving the accelerating performance of an internal combustion engine. This known fuel supply controller calculates a fuel injection rate (i.e., a fuel injection period Ti) at which fuel is to be injected by the fuel injection valve, by using a matrix memory (P.sub.B -NE map). The matrix memory is specified by engine speed Ne and intake manifold pressure P.sub.B as parameters in the normal operating mode while the engine is operating in a low load range. With the engine operating in a high load range, this controller also calculates a fuel injection rate (a basic fuel injection period Ti) at which fuel is to be injected by the fuel injection valve, by using a matrix memory (.THETA..sub.TH -Ne map) specified by engine speed Ne and throttle valve position .THETA..sub.TH as parameters. However, a disadvantage associated with this known fuel supply controller is that immediate accelerating incremental fuel supply operation using the P.sub.B -Ne map is impossible when an accelerating incremental fuel supply rate is calculated for an accelerating mode of the engine, in a range in which fuel injection rate is calculated by the PB-Ne map (such a control range will be referred to as a "P.sub.B -Ne control range" hereinafter.) This results because the detection of the intake manifold pressure P.sub.B is delayed by the effect of the length of the pipe connecting an intake manifold pressure sensor to the intake or suction pipe. Hence the detection of the intake manifold pressure P.sub.B is unable to follow the variable intake manifold pressure P.sub.B up without delay. On the other hand, when the accelerating incremental fuel supply rate is calculated in a control mode for a range in which fuel injection rate is calculated by using the .THETA..sub.TH -Ne map (such a control range is referred to as ".THETA..sub.TH -Ne control range" hereinafter), throttle valve position can be detected without delay. Accordingly, the accelerating incremental fuel supply rate varies discontinuously when the P.sub.B -Ne map is changed for the .THETA..sub.TH -Ne map as the engine is accelerated. Consequently, the engine does not operate smoothly.
The fuel supply of controller of the previously described Japanese Patent Document No. 54-134227 also detects the operating mode of the engine through the detection of the flow rate of air flowing through the intake or suction pipe, which flow rate corresponds to the degree of throttle valve opening. When the engine is in an accelerating mode, the controller increases the pulse width of fuel injection pulses for driving the fuel injection valve to increase the fuel supply rate.
However, in this known fuel supply controller, the increment of the pulse width of fuel injection pulses is set for a condition in which the throttle valve is in the initial stage of opening. The subsequent continuous increase of the rate of variation of the degree of throttle valve opening entailing increase in the rate of acceleration of the engine is not addressed. Therefore this known fuel supply controller has a disadvantage in that fuel supply control operation is delayed and the fuel supply rate cannot immediately be increased for a continuous acceleration. That is, since this known fuel supply controller decides that the engine is in an accelerating mode when the air flow rate (or the rate of variation of degree of throttle valve opening (acceleration) exceeds a single predetermined value) and performs accelerating incremental fuel supply control only once in a fixed time period for each cylinder of the engine, further accelerating incremental fuel supply control is not performed, even if the air flow rate or the rate of variation of the degree of throttle valve opening continues to increase. Consequently, fuel is not supplied at a fuel supply rate necessary for the accelerating mode. Thus, the acceleration performance of the engine is degraded. This is especially conspicuous with a motorcycle, because the degree of throttle valve opening of such an engine can forcibly be changed by the driver.